1. Field of the Invention
This invention relates to optically active ester derivatives, process for producing the same, liquid crystal composition containing said derivatives as active ingredient and light switching element employing said liquid crystal composition.
The optically active ester derivatives are useful as liquid crystal compounds, especially ones showing excellent responsiveness in video display. Further, the optically active ester derivatives can be worked into liquid crystal compositions that can be utilized as a liquid crystal element for producing a light switching element.
When the term "liquid crystal compounds" is used in this specification, it means not only those derivatives which are per se capable of forming a liquid crystal phase but also the derivatives which are useful as a component to blended for a liquid crystal even if they per se cannot be observed as a liquid crystal phase.
2. Description of the Prior Art
Image display devices utilizing liquid crystal are now widely provided for practical application, and particularly, TN (twisted nematic) type display system is popularly employed for such devices.
This system has many advantages such as small power consumption and softness to the eye because of the light-receiving type display panel which itself is not luminous, but on the other hand it has the defect that the response speed in image display is low.
High-speed response is however, especially required in the recent image displays, and many efforts have been made for improving the response characteristics of the liquid crystal compounds. However, the above-mentioned twisted nematic type display system still can not stand comparison with the luminescent type display systems such as light-emitting diode, electroluminescence or plasma displays in response time.
Efforts have been continued for finding out a new display system which is capable of high-speed response while making full use of the advantages of liquid crystal displays which are light-receiving type and low in power consumption, and one result thereof has been the proposal of a display device utilizing the optical switching phenomenon of ferroelectric liquid crystal such as disclosed in Applied Physical Letter, 36, 899 (1980).
This system utilizes chiral smectic phases such as chiral smectic C phase which shows ferroelectricity (hereinafter referred to as "Sc*"). It is known that not only the Sc*, but also chiral smectic F, G, H, and I phases show ferroelectricity.
Ferroelectric liquid crystals to be used for actually used ferroelectric liquid crystal display devices are required to have many characteristics. However, at present these requirements cannot be satisfied by only one compound and ferroelectric liquid crystal compositions obtained by mixing some liquid crystal compounds or non-liquid crystal compounds must be used for satisfying them.
Such ferroelectric liquid crystal compositions may be not only those which comprise only ferroelectric liquid crystal compounds. Japanese Patent Kokai (Laid-open) No. 61-195187 has reported to obtain ferroelectric liquid crystal compositions by mixing compound or composition which forms non-chiral smectic C, F, G, H, or I phase (hereinafter referred to as "phase such as Sc") as a basic substance with one or more compounds which forms ferroelectric liquid crystal phase, thereby to make the whole a ferroelectric liquid crystal composition. Furthermore, a report has been made to mix a compound or composition which forms a phase such as Sc as a basic substance with one or more compounds which are optically active, but show no ferroelectric liquid crystal phase to make the whole a ferroelectric liquid crystal composition. (Mol. Cryst. Liq. Cryst. 89, 827 (1982)).
From the above, it is seen that a ferroelectric liquid crystal composition can be produced by mixing a basic substance with one or more compounds which is optically active irrespective of forming ferroelectric liquid crystal phase or not. However, the optically active substance is preferably capable of forming liquid crystal phase and even if it cannot form liquid crystal phase, it is preferably one having structure which resembles a liquid crystal compound, so to speak, a quasi-liquid crystal substance. However, there have not yet been found liquid crystal materials which have spontaneous polarization necessary for high speed response and have liquid crystallinity in the lower temperature region.
Under the circumstances, the present invention provides a ferroelectric liquid crystal material which has sufficient spontaneous polarization, has high speed responsiveness and besides has liquid crystallinity in the lower temperature region.